Corrections for underwater gravimetry

Abstract

Because underwater surveys are usually conducted in coastal waters, several unique corrections are required to reduce the observed data for calculation of free-air and Bouguer anomalies. The most logical sequence for the application of corrections would be: terrain correction (if necessary) to reduce bathymetric irregularities to a flat, horizontal bottom; removal of the upward attraction of the water above the meter; free-air correction to bring the meter measurement of the surface of the reference spheroid; filling in the ocean below the spheroid with rock for a Bouguer anomaly calculation or with water for a free-air anomaly calculation. The terrain correction must be handled carefully as the bathymetric irregularities are immersed in water of finite density and, due to the close proximity of land, topographic irregularities immersed in air may be within the range of the correction graticule grid. Graticule compartment weighting factors for making this correction may be readily determined by breaking the bottom-land surface profile into several segments delimited by the gravimeter depth and the sea surface. (Author)